1. Field of the Invention
The present invention relates to the field of prosthetic appliances; more particularly, the present intention is directed to an articulated prosthetic wrist utilized as a component of a prosthetic arm.
2. The Prior Art
The technology of prosthetic arms has progressed tremendously from the era when a carved wooden arm having a hook on the end was strapped to the stump of a patient's damaged arm. In contrast, the present use of various microcircuits and small motors placed within lightweight prosthetic arms and controlled by electrodes affixed in contact with various large muscle groups, has resulted in articulated prosthetic arms capable of performing a multitude of tasks, thereby simulating to a significant extent the movements and functions of a natural arm.
Despite these overall advances in prosthetic arm technology, some components of prosthetic arms have undergone relatively little development. For example, the technology associated with prosthetic wrists remains quite rudimentary. Often, no attempt has even been made to provide any movement in the wrist region of the prothesis, and a hand is simply affixed directly to the end of the forearm of the prothesis.
Traditionally, when some type of prosthetic wrist has been used, it has typically only provided movement in one direction, such as side-to-side movement or up-and-down movement. A set pin or other securing mechanism has been used to achieve this degree of movement. Even though such one-directional movement is extremely limited, it does significantly increase the uses of the prosthetic hand and arm. Nevertheless, it will be appreciated that this type of one-directional movement is very limiting to the user and it does not provide the type of mobility and range of movement which is necessary for many functions.
In order to obtain a prosthetic wrist having some range of movement, the general approach has been to provide the hand with a small ball that is received by a corresponding socket secured to the forearm. A screw-fitting is placed around the ball and engaged with threads on the forearm to secure the ball within the socket under pressure sufficient to insure a friction fit. When the screw-fitting is tightly engaged with the threads on the forearm, the hand can be secured in the desired orientation.
Although this arrangement has been found capable of allowing orientation of the artificial hand to a variety of positions, its use has not been without disadvantages. For instance, in order to move the hand from one orientation to another, it is necessary to loosen the screw-fitting, reposition the hand, and then retighten the screw-fitting. Although this would be a simple task for a person with two hands, in practice it has been found somewhat troublesome to a person with only one natural hand.
For example, it has been found necessary to tighten the screw-fitting extremely tight in order to secure the hand in a desired position sufficiently that the hand does not move when it is used to perform a task. The torque necessary to tighten and loosen the screw-fitting has a tendency to unseat the prosthetic arm from its normal position on the patient's body, as well as being a difficult maneuver.
Additionally, after the screw-fitting has been loosened, the prosthetic hand tends to flop to a downward position due to the effects of gravity. Since the patient has only one useable hand to adjust the orientation of the prosthetic hand, it will be appreciated that it is extremely awkward to maintain the hand in a desired orientation while simultaneously tightening the screw-fitting.
The result of these problems has often been an unwillingness on the part of patients to reposition the prosthetic hand when moving from task to task, thereby rendering the need for an articulatable prosthetic wrist essentially superfluous.
Recently, researchers have attempted to utilize small motors in order to provide movement to simulate the functions of a natural wrist. Unfortunately, the use of motors in the small wrist region of the prothesis creates significant problems. For example, a larger than normal wrist has had to be historically used in order to house the motor and the associated gear mechanisms. Moreover, a significant problem is the substantial weight which is added when motors and the associated hardward are used in the prosthetic wrist. Weight is of critical importance when designing movable prosthetic arms, and the amount of weight added becomes especially important when it is placed near the distal end of the arm, such as at the wrist. The serious detrimental effects of adding additional weight has caused most developers of arms to reject the use of any type of a motorized prosthetic wrist.
In view of the foregoing, it will be appreciated that it would be a significant advancement in the field of prosthetic arms if a prosthetic wrist were to be provided that would permit simple and easy positioning of a prosthetic hand to a full range of the degrees of motion and yet would not add significant weight to the prosthetic arm. Such an improved articulated prosthetic wrist is disclosed and claimed herein.